The present invention relates to a pole tube of a solenoid actuator, for a hydraulic valve in particular and to a solenoid actuator provided with a pole tube of this type.
A pole tube of this type is described in DE 102 43 165 A1 and is a component of a pressure-tight solenoid actuator which comprises, in addition to the pole tube, a coil for actuating an armature which is guided so as to be able to move axially in an armature chamber of the pole tube, the coil surrounding the pole tube. Said pole tube substantially comprises a pole piece which can be screwed into a valve housing via a central thread, a non-magnetic intermediate piece and a tube piece which is attached thereto and is sealed at its face remote from the pole piece by means of a component which acts as a stroke limiter. The stroke limiter may also be integrated into the tube piece. The pole piece, the intermediate piece, the tube piece and the stroke limiter delimit the armature chamber for the armature which cooperates with the coil. The armature is connected to a ram or is formed as a separate part which penetrates the pole piece in the axial direction and serves to actuate a valve slide of the hydraulic valve. The non-magnetic intermediate piece acts to divert the magnetic flux into the armature.
This non-magnetic intermediate piece can be fitted in the pole tube as described in DE 197 07 587 A1 by using a bronze build-up welding process or by soldering austenitic steel, for example. When employing methods of this type, it is necessary to finish the pole tube on the inner circumferential wall delimiting the armature chamber in order to produce a smooth running surface for the armature. In order to eliminate this drawback, it is described in the aforementioned patent DE 102 43 165 A1 to thermally join the pole piece, the intermediate piece and the tube piece in such a way that a smooth running surface is produced without finishing being required. The capacitor discharge welding process (CDW) was found to be particularly advantageous as a thermal joining method, as due to the partial fusing effect, this method makes it possible to connect the components to one another without annealing and distortion.
It has been found, however, that this process may result in slight distortion of the components or an excessive thermal load on the components in pole tubes which are constructed in a complex manner or have thin walls, due to the energy introduced into the pole piece, the intermediate piece and the tube piece for the fusing process, so further finishing is required before the armature is inserted into the armature chamber. However, a finishing process of this type requires a pole tube which is open at one end, so the stroke limiter, for example, which delimits the stroke of the armature, cannot be formed in one piece with the tube piece but must be fitted subsequently.
In contrast, the object of the invention is to provide a pole tube and a solenoid actuator which can be produced simply without requiring finishing.